A Study On The Preparation And Photothermal Conversion Properties Of Carbon Nanofluids

Photothermal conversion carbon nanofluid is a kind of material that can efficiently absorb sunlight and produce heat energy.It has the potential of large-scale application in the field of solar photothermal utilization.It is still difficult to prepare carbon nanofluids with low cost and high stability,which can be used at high temperature for a long time.In this thesis,ethylene glycol(EG)based nanofluids of carbon chain nanostructure(CCNS),solvent-free nanofluids of graphene oxide,CCNS and carbon nanotubes,and modified carbon nanofluids of graphene oxide,CCNS and carbon nanotubes were prepared.Their stability and photothermal conversion properties were studied.The results are as follow.1.Stable nanofluids were successfully synthesized by dispersing CCNS in ethylene glycol through ultrasonic oscillation,and a series of nanofluids with different mass fractions were prepared.The solar absorption properties,photothermal conversion performance and thermal conductivity of the prepared nanofluids at different mass fractions were studied.The solar weighted absorption fraction of 0.05wt%nanofluid reaches 95.9%,and the photothermal conversion efficiency reaches 97.7%under one-sun irradiation.At 20°C,its thermal conductivity reaches 0.2488 W m^-1 K^-1,which is1.2%higher than that of ethylene glycol.The nanofluid is expected to be a glycol based nanofluid that can be produced on a large scale for solar energy collection and solar heat utilization.2.Solvent-free nanofluids were prepared through chemical reactions with graphene oxide,CCNS,and carbon nanotube as core materials,silane coupling agent trimethylsilyl propanesulfonic acid as corona materials,and polyetheramine M-2070 as canopy materials,respectively.The stability,thermal conductivity and photothermal conversion properties of solvent-free nanofluids were studied.The thermal conductivity of graphene oxide solvent-free nanofluid at 20°C is about 2.25 W m^-1 K^-1.After 30minutes of solar irradiation with intensity of 100 m W cm^-2,the temperature can reach43.2°C.The decomposition temperature of graphene oxide solvent-free nanofluid is300°C,and long-term use at 100°C will not affect the performance.Graphene oxide solvent-free nanofluids have the potential to be used as photothermal conversion materials.3.Graphene oxide,CCNS,and carbon nanotube were subjected to solvent-free treatment with silane coupling agent KH-560 as corona materials,and polyetheramine M-2070 as canopy materials,and then dispersed into water to prepare modified carbon nanofluids.The light absorption and photothermal conversion properties of the nanofluids with different mass fractions were studied.The results indicate that,at 1 cm optical path,the modified CCNS nanofluids of 0.025 wt%,the modified carbon nanotube nanofluids of 0.024 wt%,and modified graphene oxide nanofluids of 0.025wt%can absorb 78.1%,88.1%and 91.1%of sunlight respectively,and the photothermal conversion efficiency under solar irradiation at the intensity of 100 m W cm^-2 can reach80.6%,90.1%and 92.5%respectively.The three nanofluids also have complementary absorption spectra.The photothermal conversion performance of the three mixed nanofluids is worthy of further study.